The present invention relates to an insertable cutter tooth assembly for rotary machining tools, such as circular saws, side milling metal cutters or key seat cutters. The cutter tooth may be easily and rapidly replaced if dulled or damaged.
The circular saw for cutting wood or other materials may be chosen as one example where the present invention may be used to excellent advantage. This tool is technologically a far more sophisticated device than its outward appearance would suggest. The saw normally consists of a centrally apertured round metal plate usually provided with gullets and sharp teeth spaced around the periphery. The gullets provide a volume for accumulating and clearing sawdust produced by the teeth as they pass through the material being cut. Many versions of circular saws exist since they are used in many applications for cutting materials varying widely in characteristics. A typical circular saw will have alternating teeth designed to remove material from the left and right-hand sides of the cut being made. Only a small portion of a tooth is involved in making a cut. This results in a high-stress loading and high wear factor which necessitates frequent resharpening and/or repair. To reduce this need involving downtime, hardened teeth are frequently used. It is not desirable to harden the entire blade since this normally induces an unacceptable brittleness. The body of the saw, or sawplate as it is normally called, is usually made of a tough but relatively soft metal that can withstand considerable bending and twisting from load-induced stresses. Additionally, the larger sizes are normally prestressed by hammering and peening to induce a built-in tension or "hoop stress" into the rim area of the saw.
Replaceable teeth have been in use with circular saws for over a century. These teeth have been an answer to the need for widely differing metal properties in the sawplate and at the point at which the cut is made. Inserted teeth are locked into the periphery of the sawplate by a number of differing arrangements. They are normally made of hardened steels, although cemented carbides are also occasionally employed. Alternatively, hard teeth may be brazed to appropriate locations on the perimeter of the saw, or to the tips of inserted teeth. Brazed teeth are almost universally cemented carbides since brazing temperatures normally lower the hardness of steels. It is common practice for both inserted teeth and brazed teeth to be sharpened in place on the sawplate. Alternatively, depending on the particular construction for locking the tooth in place, inserted teeth may be removed and sharpened separately. This is not normally done except when tooth replacement is necessary since the locking mechanisms tend to be relatively complex and are often riveted or semi-permanently fixed into position.
The following United States Patents can be sited as exemplary of known insertable teeth that have some relationship to the present invention. U.S. Pat. Nos. 2,736,352 (Wright), 2,746,494 (Cox), 2,978,000 (Raney), show insertable replaceable teeth for chainsaws but have some commonality with the present invention. Each of these inventors uses a tooth having a head portion attached to a rearwardly extending shank. In turn, the shank is forced by a friction fit into a socket formed on a modified cutter link plate. The Wright saw tooth assembly uses a round cup-shaped tooth in which edge orientation relative to the chain is not critical. In the Cox tooth, the rear surface of the head has protruding nibs that engage corresponding notches in the socket in order to ensure proper orientation and prevent rotation. The shank of the Raney tooth has a ridge which engages a longitudinal slot formed in the socket to serve the same function. Wright also shows versions of his structure which can be used on round or band saws. Here, the socket that holds the tooth is formed in a bent strip of sheet metal which, in turn, is permanently riveted to the sawplate. The inventor notes that this tooth holder may be bifurcated to straddle the saw blade. He further shows a tooth shank having a converging taper away from the head portion. Another inserted tooth for circular saws is shown in U.S. Pat. No. 2,994,350 (Lundberg). Here a strap is riveted to the outer perimeter of one of the buttresses or "tooth roots" so as to form a socket structure. The shank portion of an insertable tooth is then pressed into the socket where it is held by a spring mechanism. The tooth abuts against a shoulder on the buttress which helps to retain it in position when subjected to operating stresses.
The teeth of Wright and Lundberg are used on circular saws with the axis of the shank portion lying generally tangent to the circumference of the saw. Radially inserted teeth are shown in the similar U.S. Pat. Nos. 579,383 (Coyle) and 912,774 (Aupperle et al.). In both of these a locking strap is formed around the buttress between gullets. The strap is retained by one or more locking structures on the gullet. In turn, the tooth is inserted essentially radially along the leading edge of the gullet where it is held by the strap. A number of interlocking elements retain the integrity of the arrangement. However, the teeth cannot be readily removed without prying open and potentially destroying the retaining strap. U.S. Pat. No. 540,065 (Krieger) shows a replaceable tooth similar to Lundberg's but oriented radially and retained with a rivet or locking pin.
Examples which span a century of development showing more conventional, semi-permanently inserted teeth are seen in U.S. Pat. Nos. 207,003 (Berry) 2,422,111 (Lundberg) and 4,257,302 (Heimbrand). Other structures worthy of note are Tyler, U.S. Pat. No. 14,172 and Kolesh, et al., U.S. Pat. No. 3,633,637. Kolesh, et al. show inserts comprising several teeth which are tightly riveted into a T-slot machined into the circumference of a round sawplate. This group of patents is more noteable as an example of historical development than it is of close pertience to the present invention.
One problem with many of the known inserted teeth is that during use they tend to act as wedges serving to detension the outer rim of the sawplate. Further, as noted previously, many are difficult to replace and involve the removal of rivets or retainers. Further, few of the inserted tooth types which have stood the test of time are replaceable at the point of use if dull or damaged. Common practice is to remove the entire sawplate, transport it to the filing room and replace it with a similar sharp saw. Saw replacement can involve considerable loss of productive time.